New Haven Register (New Haven, CT)
Over time, dino skulls changed at earlier ages
NEW HAVEN — They lived 150 million years ago.
But the sauropods still capture our attention. (Think Brontosaurus.)
In this case, it’s because a new study at Yale University of giant dinosaurs, which evolved in a specialized fashion compared to smaller species, shows that the specialized adaptations in the skull occurred in younger and younger dinos as they evolved.
Sauropods, which include Brontosaurus, Apatosaurus and Brachiosaurus, were giant, plant-eating dinosaurs that lived in the late Triassic through late Jurassic periods, 150 million years ago. They were named by Yale paleontologist O.C. Marsh in 1878.
The sauropods had a unique skull structure, according to a release on the study. Their nostrils, elongated faces, the backs of their skull and jaw muscles evolved over time, possibly to enable them to feed both in the trees and on the ground.
“Every part of the sauropod body is enormously modified, compared to other dinosaurs. Their skulls are no different. But no one had parsed out how and when those skull modifications happened,” said Yale paleontologist Bhart-Anjan Bhullar, senior author of the study, which appears in the journal Evolution.
Bhullar is an assistant professor in the Department of Earth and Planetary Sciences and assistant curator at the Yale Peabody Museum of Natural History.
By studying sauropod fossils at different ages, the researchers were able to see that, over time, features that appeared in adult dinosaurs gradually began to appear in younger animals, according to the release.
The study of the growth of an individual from youth to adulthood is known as ontogeny and the study of the structures of the body is morphology. In order to study how those structures changed as the sauropod aged, “multiple individuals of different ages are needed to understand how developmental changes happen within species and among species in an evolutionary framework,” said first author Matteo Fabbri, a doctoral student in the Department of Earth and Planetary Sciences.
By using micro-CT scanning, the researchers created three-dimensional models of sauropod skulls — including two skulls of Anchisaurus, a sauropod precursor species that Marsh found in Connecticut in the 19th century and brought to the Peabody.
In Anchisaurus, the juveniles of the species resembled earlier dinosaurs and developed their unique skulls as adults, according to the release. But as later species emerged, the same features were found in embryos and juveniles.
“This is the first time this process, which is called predisplacement, has been demonstrated convincingly among dinosaurs, and one of the few times it has been demonstrated in the fossil record,” Fabbri said. “Ultimately, we show how different groups of dinosaurs evolved different developmental strategies.”
“It’s a key, missing component in our understanding of how these massive, elongated creatures came to be,” Bhullar said. “It also is a rare demonstration of the way in which changes in developmental timing break constraints and allow the evolution of extremes of form and function — in these, perhaps the most extreme of all land animals.”